In This Section
Journal of the AES
2013 March - Volume 61 Number 3
Spatial Distribution of Signals Emitted by a Sigma-Delta Modulation-Driven Linear Digital Transducer Array
Combing sigma-delta modulation with digital drivers in a loudspeaker array adds an extra dimension of flexibility because a smaller number of transducers can each be driven with a unique digital signal. The drive signal is effectively a vector. This architecture has the advantage of high integration, smaller size, lower cost, and improved electroacoustic efficiency. Based on simulations and experiments, it is clear the various performance metrics, such as sound pressure level, signal-to-noise, and harmonic distortion, are a function of the spatial angle relative to the midline. Because of the differences in acoustic path length, the quantization noise in the channels may no longer cancel at some angles.
The time required for measuring the spatial features of sound sources and receivers can be decreased by using test signals composed of multiple exponential sweeps. But any such technique must include the influence of nonlinearities at modest signal levels. This research expands on a strategy to overcome interference between the components created by system nonlinearity and those that are part of the system impulse response. Previously, the so called multiple exponential sweep method (MESM) has been proposed using a combination of the two strategies, overlapping and interleaving. This method is modified by introducing a generalized overlapping method and further consideration of the fine structure of the impulse responses to be measured. This method can yield shorter measurement times than the original method without loss of accuracy.
This research evaluates four state-of-the-art acoustic feedback cancellation systems in hearing aids in terms of the cancellation performance, sound quality degradation, and computational complexity. The authors compared a traditional full-band system to a system with a prediction error method in a full band, a subband system, a subband system with frequency shifting, and a recently proposed subband system with a novel probe noise deployment. All systems outperformed the traditional full-band system in cancellation performance, especially the subband system with probe noise is most effective for cancellation. However, in all cases there was a trade-off between performance and computational cost. With a 3-times increase in computation load, the probe noise based cancellation system can be realized that functions even in the most challenging feedback situation.
In some situations, sound measurements must be made in a space when a live audience is required to be present. For applications such as a ground-stacked array (a transducer component of a multiple component sound reinforcement system), this component cannot be excited in isolation because other transducers are also active during the concert. Two simple methods are proposed for obtaining the subwoofer’s impulse response: the desired impulse response is obtained by subtracting the separate measurements made with and without subwoofer, or a small delay is added to the subwoofers' signal such that the impulse response is then calculated from the difference with and without the delay. Both methods allow relatively fast and unobtrusive measurements of the subwoofers. Both show good repeatability.
Standards and Information Documents
AES Standards Committee News
Measurement of sound systems in rooms; measurement of loudspeaker drive units; plane-wave tubes—design and practice
134th Convention Preview, Rome
Networks are increasingly used to transfer audio data, instead of using dedicated audio interfaces. Open IP-based protocols are one possible solution, provided that interoperability issues can be tackled successfully. The AES-X192 project builds on that approach. On the other hand, the AVnu Alliance has been set up to certify interoperability between devices that work using the AVB standard, which currently operates at a lower level in the network hierarchy. New business opportunities exist in both domains.
135th Convention, New York, Call for Papers